Actually, sdl-config (for SDL1) seems to be equally broken.  Both are bash
scripts.  Here is an excerpt:

--8<---------------cut here---------------start------------->8---
#!/gnu/store/q19l04vd2za80mk1845pz7r8cz29qk43-bash-minimal-4.4.23/bin/sh

prefix=/gnu/store/np2g3p3k2wsjgd3g5ly3hdabls49xyq4-sdl-1.2.15

#...

while test $# -gt 0; do
  case "$1" in
  -*=*) optarg=`echo "$1" | LC_ALL="C" sed 's/[-_a-zA-Z0-9]*=//'` ;;
  *) optarg= ;;
  esac

  case $1 in
	# ...
    --cflags)
      echo -I${prefix}/include/SDL -D_GNU_SOURCE=1 -D_REENTRANT
			# ...
--8<---------------cut here---------------end--------------->8---

The paths are hard-coded.

We could patch sdl-config and sdl2-config to make the path relative to the
script.  That would work I guess.

It's a rather stupid script and I don't understand it's purpose.  Why not using
pkg-config?

We should report upstream.

-- 
Pierre Neidhardt
https://ambrevar.xyz/